Recording potentiometer



' Jan. 19, 41932. F. Fl EHLIN'G v 1,841,558

RECORDING POTENTIOMETER Filed July 5, 1929 3 Sheets-Sheet 2 Jan. 19,1932. F. F. UELING l l 1,841,558

` RECORDING POTENTIOMETER Filed July '3,1929 3 sheets-sheet 3 mf ya 109fb l 1d f V 52 525m: /ob 12100. 55C

D3 DL D1 g1 /ssb G INVENTOR4 the recor ing element as Patented Jan. 19,1932 PATENT OFFICE FRITZ FREDERICK UEHLING, OF PASSAIC, NEW JERSEYRECORDING POTENTIOMETER i Application led July 3, 1929. Serial No.375,668.

This invention relates to improved means for measuring and recordingtheelectromotive force of a thermo-couple, or any other electro-motiveforce by balancing a potentiometer against said force. The potentiometeris actuated by a motor, the operation of which is controlled by a novelform of galvanometer in combination with specially designed relays, allas hereinafter described in detail.

One of the specific objects of this invention is to provide agalvanometer which may be located at a distance from the potentiometerand which at the same time may control the operation of two or morepotentiometers, each otwhich measures and records the fluctuations ofindependent electro-motive forces from different sources.

I attain these objects by sthe mechanism illustrated inthe accompanyingdrawings in which- Figure 1 illustrates all of the essential parts ofthe'invention for a single measurement; Figure 2 is a cross sectionthrough line 2--2 of Figure 1 to illustrate the relation between theslide wire of the potentiometer, the slide wire shoe, the recording pen,and the drum on .which the record is produced; Figure 3 is an elevationof relay R-l of Figure 2; Figure 4 is a cross section on line 4-4 ofFigure 2 to illustrate on an enlarged scale, the relation between theslide wire, the slide w1re shoe and the shoe uide;.Figure 5 is an endview o illustrated in Figa commuure 1; Figure 6 is a plan view of of.similar tator and one of a Amultiplicity switches actuated thereby forclosing the proper circuits to measure the electro-motive forcefromdi'erent sources; Figure 7 is an elevation of the electrically operatedswitches in Figure 6; Figure 8 is a cross section on the line 8-8 ofFigure 6: Figure 9 is a diagram-- matic view of a multiplicity'ofindependently operated potentiometers for makingl 1ndependent records,and includes the vauometer with the-necessary connections for operatingeach of them.

Similar numerals referto similar parts throughout all offtheillustrations.

A motor 1, Figures 1 'and 5, is in geare connection with a cylinder onwhich the slide.

wire 5 of the potentiometer is spirally wound, as illustrated. Thecylinderis mounted on a shaft 3, which is rotatably supported by a:trame 26, and is connected with the motor 1 through a reduction gearl104,v the motor 1 56 being fastened to the frame 26 by means of .abracket 25. The circuits which include the slide wirey 5 are connectedtherewith through rings 6, 7 and 112, against which rest electriccontact One extreme'end of the slide wire 5 is connected with the ring7, while the'other extreme end is connected with the ring 112. A slidewire shoe 24 may be shifted, in a manner to be'presently described,throughout the 65 entire length of the wire 5. The ring 6 iS connectedwith a fixed point 9 on the wire 5 by means of an imbedded wire 32. Itthus follows that if a current flows through the wire 5 from ring 7 toring 112, there will be 70 a drop in Vpotential across said wire betweenthe point 9 and the shoe 24. It is this drop, which can be changed-byshifting the shoe 24, that I utilize to balance the electro-motive forceto be measured. The curvature of the rubbing surface of the shoe 24' isconcentric with the spiral form of wire 5, as illustrated in Figure 2.It is also grooved to it the wire itself, as illustrated on an enlargedscale in Figure 4. In other words, the shoe 24 has a groove which tsover the spirally wound wire and serves as a female thread, while thespirally wound wire Y serves as a male thread over which the shoe 24fits. A iat spring 22, of the proper curva- 85 ture is fastened to theshoe 24 and rests against a guide rod 23, Figure 1, thus holding theshoe tightly against the wire. The spring 22 is cut out at each end tofit the rod 23, as illustrated in Figure 2. It thus follows that as ,thecylinder on which the wire 5 is wound, is rotated in one direction orthe` other by the motor 1, the shoe 24 will shift to the left or to theright, depending upon the direction in which the motor is operi ated.The rod 23 is insulated from the -rame 26, at-30 and 31 thus permittingthe measurement of the drop across Wire 5'between the point 9 andthe-shoe 24 without the fear of short circuiting through the frame 26.1c

brushes 10, 11, and 12 respectively. 60

The current which passes through the spirvally wound wire 5 starts atbattery 14, asses ampere meter through wire 18 and brush 12 y to ring112, from the ring 112 through the spirally wound wire to the ring 7,and from the attery, thus completing the circuit.

That partof the spirally wound wire 5 be.

tween the Vfixed point 9 and the shoe 24 forms part of the. circuitwhich includes the galvanometer andthe source of the electro-m0- tiveforce to .be measured. The source of electromotive"force which has beenchosen to illustrate this invention is a thermo-couple 59, while thegalvanometer G is of novel form, the details of which will be presentlydescribed. The circuit which .includes the couple,starts at couple 59,thence through wire 60 and brush 10 to ring 6, from the ring 6 throughthe imbedded wire 32 to the point 9, from the point 9 'through thespirally wound `wire 5 to the shoe 24, from the shoe 24 through aflexible wire 61 and wire 62 to the binding post 63 of the galvanometerG, from the` binding post 63 through wire 64, the pivoted coil 65 of thegalvanometer, and wire 66 to the connection 33, from the connection33through a resistance 67 tol a connection 88, from connection 88 throughwire 68 A to binding post 69, and from binding post 69 through wire 70back to the couple, thus completing the circuit. v

The galvanometer G is illustrated in more or less diagrammatic form. Thecoil is pivoted in the usual manner, not shown, and carries anindicating needle 72, which is electrically connected with the wire 66.The indicating needle 72 serves as one member of a contact mechanism foractuating one or the otherl ofthe relays R-1 and R- 2. The circuit whichincludes the relay R-l is closed when the needle makes contact with thecontact screw 77, and the circuit which yoperates relay R-2 is closedwhen contactis made between the needle and contact screw 76. The specialmanner in which these relays function will be presently described. Thecontact screws 76 and 77 are carried by 75 and 78 respectively and areinsulated from the galvanometer and from each other by insulation pieces73 and 74. The resistance 67, al-

ready referred to, forms a very important element of this -invention andwill bev described in further detail later.

Therelay R-l consists of a pair of electromagnets 42 permanentlyfastened'to a base plate 220 by means of bracket 43. An armature 34,Figures 1 and 3, with which the magnets react, is fastened to 'a shaft37, which shaft is carried by bearings 38 and 39. Twd mercury switches40 and 41 are also fastened to this shaft. These mercury switches are ofthe well-known form which permits the ring)7 through brush 11 and wire13 back to closing of a circuit when they are tilted in one directionand the opening of a circuit when they are tilted in the otherdirection. The armature 34 is held in its normal position against a stop35by means of a spring 36, both the spring and stop being supported by abracket 44. The mercury switches 40 and 41 are so fastened to the shaft36 that when the armature 34 is in its normal position, as illustrated,the circuit through the switch 40 will be open and the circuit throughthe switch 41 will be closed, and when the armature 34 is pulled out' ofits normal position by reaction with the magnets 42, the circuit throughthe mercury switch 40 will be closedv and vthe circuit through themercury switch 41 will be open. In other words, when the magnets 42 areenergized the tilting effeet of the .armature will close the circuitthrough switch 140 and open the circuit through switch 41, and when themagnets 42 are de energized the spring 36 will bring the armature backto its normal position in which case the circuit through the switch 40will be open and the circuit through the switch 41 will be closed.

Relay R-2 is of the same construction as relay R-1. The mercury switch84 of relay R-2 corresponds with the mercury switch 41 of relay R-1, andthe mercury switch 221 of'relay R-2 corresponds with the mercury switch40 of relay R-1. The purpose of the mercury switch 221 is to close thecircuit which operates the motor 1 in one direction, while the purposeof the mercury switch 40 is to close the circuit which operates themotor 1 in the opposite direction. These circuits will be referred tolater.

The circuit which includes the switch 41 of relay R--l starts at battery93, thence through wire 94 to binding post 47, from binding post 47through flexible connection 95, mercury switch 41 and lexible connection96 to magnets 42, from magnets 42 through wires 97 and 90 to bindingpost 46, from binding post 46 through wire 98 to binding post 69, frombinding post 69 through wire 68, resistance 67 and wire 66 to theindicating needle 72 and, when the indicating needle touches contactscrew 77 back to the battery n Words, aslong as the needle 72 touchesthe contact screw 77` so long will the armature fiexible connection 83,mercury switch 84 and flexible connection 85 to magnets 86, from magnets86 through wirel 87 to binding post 57, from binding post 57 throughwires 89 and 90, to binding -post 46, from binding post 46 through wire98 to binding post 69, from binding post 69 through wire 68, resistance67 and wire 66 to the indicating needle 72, and when the needle 7'2touches the contact screw 76, back to the battery 8l through wire 79-andbinding post 80, thus completing the circuit. It thus follows that whenthe needle 72 touches the contact screw f 7 6, magnet 86 will beenergized thus tilting the switch 84 which immediately breaks thecircuit. As soon as the circuit through the mercury switch 84 has beenbroken, the armature and the mercury switches will be brought back totheir,` normal position, as illustrated, in which case the circuitthrough switch 84 will again be closed and the cycle will repeat itself.In other words, as long as the needle 72 touches the contact screw 76,so long will the ,armature and mercury switches of relay R-2 continue tooscillate.

In further reference to the galvanometer G, it is obvious that the forceof the delicate needle of a galvanometer is not suflicient to makereliable contact without the use of some external force. In the ordinaryrecording galvanometer the indicating needle is utilized to closeelectrical circuits by the assistance of some outside force, as forexample., a depressor bar which is brought into place at regularintervals. It is through the use ot the resistance 67 that I eliminatethe use of similar mechanical m'eans. lustrate the function of theresistance 67` let us assume that the needle 72 has been deflected, justsuliicientlyf to touch the contact screw .77. In such a case the contactresistance between the needle 72 and the contact screw 77 would be'toohigh to allow suf- `tcient flow to actuate the relay R--l in the manneralready described. It is obvious, however, that some current of very lowmagnitude will flow, even though it be not suicient to actuate therelay. This flow throughl this circuit which includes the'resstance 67,regardless of its low magnitude, will cause a drop in potential acrossthe resistance 67, which drop will cause a flow through the circuitwhich includes pivote'd coil 65, wires 64, 62 and 61, shoe 24, 'thespiral wire of the potentiometer between 24 and the point 9,-w-ires 32,60. the thermo-couple, and wire 70. The battery 93 is of such a polaritythat this additional iow through the pivoted coil 65, as caused by thedrop across the resistance 67,

To ilwill increase the tension of the needle 72 against the contactscrew 77. As soon as this tension has been increased, the flow throughthe needle 72 and the resistance 67 will also increase, and as this ilowincreases, the increased drop in potential across the resistance 67 willstill further increase the flow through the pivoted coil 65, therebystill further increasing the tension of the needle 72 against thecontact screw 77. In other words as soon as the slightest contact hasbeen made between the needle 72 and the contact screw 77, the mechanicalforce between the needle 72 and the contact screw 77 will be built upalmost immediately to a point where sufficient current willflow throughthe needle to actuate the relay REI.

Similarly let us assume that the needle 72 has been deflected justsufficiently to touch the contact screw 76. In such a case the contactresistance between the needle 72 and the contact screw 76 will again betwo high to allow sutlieient flow to actuate the relay R-2 in the manneralready described. It is again obvious, however, Athat some current ofvery low magnitude will flow, even though it be not sufficient toactuate the relay. This flow,

through the circuit-which includes the resistance 67, regardless of itslow magnitude, will cause adrop in potential across the resistance 67,which drop will cause a flow through the circuit which includes pivotedcoil 65, wires 64, 62 and'61, shoe 24. the spiral wire of thepotentiometer between 24 and the point 9, wires 32. 60, thethermo-couple. and the wire 70. The battery 8l is of opposite polarity7to that of battery 93 and such that the additional flow throughthepivoted coil 65, as caused bythe drop across-the resistance 67 willincrease the tension of the needle 72 against the contact screw 76. 1 Assoon as this tension has been increased. the flow through the needle 72and the resistance 67 will also increase, and as this iiow increases`the increased drop in potential across the resistance 67 will stillfurther increaselthe fiow through the pivotefl coil 65, thereby stillfurther increasing the tension of the needle 72 against the contactscrewr76. In other words. as soon as the slightest contact has been madebetween the needle 72 and contact screw 76, the mechanical torce betweenthe needle 72 and the contact screw 76 will be'built up'almostimmediatelyy to a point where s'uicient current will flow through t-heneedle to actuate the relay R-2.

It will be notedthat the batteries 8l and 93 are of diii'erent polarity.'lhis is an important feature of the invention since the drop inpotential across the resistance 67. it 1 ,221, and wire 108 the needleand the screw has been made. Likewise the drop in potential across theresistance 67, if caused by battery 8l, must be of the opposite polarityto cause Va flow through ,the pivoted coil 65, in the manner alreadystated, to force the 4needle 72 tighter against the contact screw 76after the initial contact between the needle 72 andthe contact' screw 76has been' made.

To further illustrate the operation of the apparatus, let us assumethatthe dro in potential between the shoe 24 and the point 9, as caused bythe How from battery 14, exactly balances the electro-motive force fromthe thermo-couple 59.. In such a case the flow through the pivoted coilofthe galvanometer will be zero, the'needle 72 will be in zero position,as illustrated, in which case it touches neither of the contact screws76 or 77. However, if the ,electro-motive force of the thermo-coupleincreases, the needle 72 of the galvanometer will be deilected in aclockwise direction against the contact screw 76. As soon as thisoccurs, a delicate electric flow will be permitted through the needle72, wire 66, the resistance 67 wires 68, 98, 90, 89, 87, magnets 86,mercury switch 84, wire 82 and battery 81. Although this delicate flowmay not be sufficient to actuate the relay, it will never theless causea drop across the resistance 67, which drop, in the4 manner alreadystated, will build up a pressure between the needle 72 and the contactscrew 76 until there is suficient ow'to tilt the armature and mercuryswitches of relay R-2. As soon as the mercury switch 221 has been tiltedby the magnet, the circuit through the motor 1 to operate it 1n a givendirection will be closed. This circuit starts at A,battery 52 andcontinues through wire 51, wire 105, mercury switch to motor 1 and lfrommotor l back to the battery through wire 53. The motor 1 is so woundthat when the circuit through the mercury switch 221 is closed it willrotate the cylinder on which the wire 5 1s splrally wound, in the properdirection to move the shoe 24 toward the right in the manner described.As previously stated, as soon as the mercury switches have been tiltedby the magnet 86, the circuit through the switch 84 will be brokenthereby permitting the mercury switches to come back to their normalposition, as illustrated'. This cycle w1ll repeat itself as long as theindicating needle 2 touches the contact screw 76. By virtue of theconsecutive closing and` opening of the mercury switch 221 it is obviousthat the motor 1 will cause the contact shoe 24 to move to the right aslong as the relay R 2 continues to oscillate. As the shoe 24-moves`toward the right, the drop across the spiral wire 5 between the point 9and the shoe 24 will increase until the point has been reached wherethis drop a in balances the electromotive force of tg; couple, in whichcase needle 72 of the galvanometer will again assume its zero position,as illustrated, the oscillation of relay R2 will cease and the motorwill stop.

Likewise if the electro-motive force of the thermo-couple decreases, theneedle 72 of the galvanometer will be deflected in a counterclockwisedirection against the contactscrew 77. As soon as this occurs, adelicate electric Iflow will be permitted through the needle 72,

wire 66, the resistance 67, wires 68, 98, 90, f

97, magnet 42, mercury switch 41, wire 94 and battery 93. Although thisdelicate flow may vnot be sufficient to actuate the relay, it willVmotor 1 back to the battery through wire 53. .The motor l is so woundthat when the circuit through thel mercury switch 40 is closed it willrotate the cylinder on which the wire 5 is spirally wound, in the properdirection to move the shoe 24 toward the left in the manner described.As previously stated, as soon as the mercury switches have been tiltedby the magnet 42, the circuit through the switch 41 will be broken,thereby permitting the mercury switches tocome back to their normalposition, as illustrated. This cycle will repeat itself as long as theindicating needle 72 touches thecotact screw 77. By virtue of theconsecutive closing and opening of the mercury switch 40 it 1s obviousthat the motor 1 will cause the contact shoe 24 to move to the left solong as the relay R-l continues to oscillate.l As the shoe 24 movestoward the left, the drop in potential across the spiral wire 5 betweenthe point 9 and the shoe 24 will decrease until the point has beenreachedwhere this drop again balances the electro-motive vforce of thecouple, in which case the needle 72 of the galvanometer will againassume its zero position, as illustrated the oscillation of relay R-1will cease and the motor will stop.

It is obvious from the above that the shoe 24 will move from left toright or vice versa in exact proportion to any change in theelectro-motive force of the couple. I therefore provide a pen arm 19which is fastened to the shoe 24,' as illustrated in Figures 1, 2, and5. At the end of the pen arm is fastened a pen or marker 20 which restsagainst a paper chart wound on a cylinder 21. The cylinder is mounted ona shaft which is supported by bearings 28 and 29 and is rotated atl aconstant velocity by a clock movement 27. It thus follows that a curvewill be automatical- `ly drawn showing all variations in the eleca givenelectro-motive force may thus be changed by adjusting the variablerheostat 15.

Figure 9 illustrates an arrangement for actuating a multiplicity ofrecording units, each measuring independent electrical variables and allcontrolled by a single galvanom'eter G. The four recording units V, lV,

X, and Y, as illustrated, are operated respectively by motors 1a, 1b,lc'and 1d. Each recordmg unit consists of a spirally woundpotentiometer, the same as already described and illustrated inFigure 1. The first recording unit V has its wire. 5a spirally wound son a cylinder which isrotated by the motor 1a with which it is in gearconnection through a chain drive 184. Similarly the rotatable cylindersof the recording units W, X, and Y are' operated respectively by motors1b, 1c, and 1d through the chain drives 19T, 198 and 199. In order toeliminate a redescription of each recording unit, I have utilized thesame numbers for similar parts as used in Figure 1, except for the factthat the numerals of recorders V, lV, X, and Y have the suflixes a, b, cand d respectively. The only difference in these recording units and therecording unit illustrated in Figure 1 Vis the chain drive alreadymentioned and a novel method of supplying electric current to each ofthe potentiometers from a single source 14. The manner in which this isaccomplished will be presently described. The numerals referring thegalvanometer G and relays R-l and R-2, Figure 9, and such other parts asare used in connection with each of the recording units, are the same asin Figure 1 soas to further simplify this description.

D1, D2, D3, and D4 are each three-pole switches to be referred to laterwhich, one at a. time, connect the galvanometer G and relay R-l andrelay .l-2, Figure 9, with the recording units V, W, X, and Yrespectively, already above referred to. The three-pole switches, D1,D2, D3 and D4 are electrically actuated by a commutator in such a waythat the actuating circuits are consecutively closed so that only one ofthe switches is closed at a time. The three-pole electrically o peratedswitches D1, D2, D3 and D4 may be of any form, but as a matter ofconvenience I have illustrated a form which consists of a pair ofmagnets143, Figures 6 and 7, fastened to a base plate 223. The magnet isprovided with an armature 180, Figure 7, which is fastened to two arms171 and 172. These arms are carried by bearings 124 and 125 and thearmature is normally held in a fixed upright position by means of aspring 176, Figure 7. The fixed upright position of the armature isdetermined by the stop 173 against which the arm 172 rest-s due to thetension of the spring. Extensions 150, 158 and 166 are fastened to thearmature, as illustrated, and are insulated from it and from each otherby means of the insulation piece 170. Contact pieces 149, 157 and 165are provided with which the extensions 150, 158 and 166V respectivelymake electrical contact when they are depressed by the action of themagnet 143. The contact pieces 149, 157 and 165 are respectivelysupported by insulation uprights 148, 156 and 164. It

'thus followsthat three independent electrical connections, onebetweenthe binding posts 14.7 and 152, one between the binding posts 155and 160, and the other between the binding posts 163 and 168 will bemade when the magnets 143 are energized, and broken when the magnet isdeenergized.

A commutator C, Figure 6, is provided, which automatically closesconsecutively four such switches D1, D2, D3, and D4, Figure 9,

already referred to. The commutator C, Figure 6, consists of a shaft 125properly supported by bearings, on which four rings 113, 114, 115 and116 are respectively connected with the segments 129, 130, 131 and 132of a commutator, a cross section of which is illustrated in Figure 8.The rings 113, 114, 115 and 116 are respectively provided with electriccontact brushes 120, 119, 118, and 117. The brushes are respectivelysupported by insulation posts 121,` 122, 123, and 124. Another electriccontact brush 128 is provided for the segments of the commutator and issupported by an insulation piece 127. It will be noted that the segmentsof the commutator are not concentricy with the axis about which theyrevolve. This condition is purposely provided so that `at no time willthe brush touch more than one of the segments. The shaft 125 whichsupports the commutator, is driven by a clock 126 or by any ,othermotive means in a counter-clockwise direction. The brush 128 is in theform of a spring which rests on one segment at all galvanometer G andrelays R--l and R-2 in Cil CII

`D3 and D4 are closed 'the same way as illustrated in Figure 1 and willautomatically record the electro-motive force of the couple 59a. If theelectro-motive force of the couple 59a is balanced by the drop acrossthe potentiometer between the point 9a and the shoe 24a there will be nochange in the position of the pen arm 19a. On the other hand, lif thereis a change in tne electro-motive force of the couple 59a since theswitch D1 was last closed, the penvarm 19a will adjust itselfaccordingly and in the manner already described. Similarly if thethree-pole switches D2, D3, and D4 are consecutively closed bycommutator C not shown in Figure 9, the pen arms 196, 190 and 19d willadjust themselves as required to balance .any change in theelectro-motive forces from the couples 596, 59e and 59d respectively.Only one of the three-pole switches D1,-` D2, at a time. By means of thecommutator, already referred to, these three-pole switches will closeconsecutively for a period of about one quarter of a minute, thus makingit possible for the pens 19a, 196, 190 and 19d to adjust themselves Vtothe electro-motive force of their respective couples at regularintervals.

In the position illustrated, Figure 6, the brush 128 is in contactwiththe segment 131. In this position the circuit through the magnet 143 isclosed. The action of this magnet closes switch D thus connecting thepost 147 with post 152, the post 155 with post 160, and the post 163with the post 168, all as previously described. This circuit 'whichclose-s the three-pole switch D starts at battery 138 thence throughwires 139 and 140, to binding post 141, :trom binding post 141 throughmagnet 143 to binding post 144,l from binding post 144 through wire 145to brush 117, from brush 117 through ring 116 to segment 135, and thencethrough the brush 128, and wire 137 back to the battery. As thecommutator rotates, the brush 128 will consecutively come in contactwith the segments 131, 132, 133 and 134, thus respectively closing thecircuit through the electrically operated switches D1, D2, D3, and D4 ofFigure 9. The circuit which closes the switch D1 includes the brush 117and wires 145 and 140, Figure 6, as described, while the circuits whichsimilarly close the switches D2, D3 and D4 respectively include thebrush 118 and wires 145 and 181, the brush 119 and wires 145 and 182,and the brush 120 and wires 145 and 183.

The electric current through the potentiometers of the recording vunitsV, W, X and Y, Figure9 come from a single source already mentioned. Thesource of current is la battery 14, from which the current Hows throughthe wire 13, Figure 9, to ring 7a1of recording unit V, from ring 7athrough the spirally wound wire 5a to ring 112e, from ring 112e throughwire 210 to ring 76 of recording unit Leagues A W, from ring 76 throughthe spirally wound wire 56 to ring 1126, from ring 1126 throu h wire 209to ring of the recording unit from `ring 7c through the spirally woundwire 5c to the ring 1120, from the ring 1120 through wire 208 to ring 7al of the recording unit Y, from the ring 7d through the spirally woundwire 5d to ring 112d, from 112Z through wire 18 -to the milliamperemeter 17, and from the milliampere meter 17 through wire 16 and theadjustable resistance 15 back to the battery. In order to establishdifferent calibrations for the recording units V, W, X and Y, I cause adiierent rate of electric flow through the wires 5a, 56, 5c and 5drespectively. This is accomplished by shunting variable resistances 187,188, 189 and 190 across the 'respective pote'ntiometers, as illustrated.The variable resistance 187 is connected with the rings 7a and 112athrough the wires 200 and 201 respectively. 4Likewise the variableresistances 188, 189 and 190 are respectively connected with rings 76and 1126, rings 7c and 1120, and rings 7d and 1120 through wires 202 and203, wires 204 and 205, and wires 206 and 207. It thusfollows that ftheratios between the calibration of units V, W, X, and. Ycan be definitelyestablished by adjusting the respective resistances 187 188, 189 and 190an'd the constant electric flow to establish the desired calibration canbe maintained by adjusting the variable resistance 15` as required tokeep the needle of the amperefmeter 17 at a fixed point.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. In a device of the class described, the combination with apotentiometer, of a galvanometer, a resistance, a circuit which includesthe potentiometer, the galvanometer .and the resistance, and a circuitcontrolled by thegalvanometer which includes the resistance.

2. In a device of the class described, the combination with apotentiometer, of a galvanometer, a resistance, means for actuating thepotentiometer in one direction, means for actuating the potentiometer inthe opposite direction, a circuit which includes the potentiometer, thegalvanometer and the resistance, a circuit controlled by thegalvanometer which includes the first actuating means and theresistance, and a second circuit controlled by the galvanometer whichincludes the second actuating means and the resistance.

3. In a device vof the class described, the combination-with agalvanometer having an indicating needle, of a contact piece with whichthe needle makes electrical contact when deflected in one direction, asecond contact piece with which the needle makes elecpotentiometer, thegalvanometer and the resistance.

4. In a device of the class described, the combination with agalvanoineter having a pivoted coil and an indicating needle, of a re-vsistance, a source of electro-motive force, a potentiometer, an electriccircuit which includes the potentiometer, the pivoted coil, theresistance, and the source of electro-motive force, a contact piece withwhich the needle makes electrical contact when defiected in onedirection, a second contact piece with which the needle makes electricalcontact when deflected iii the opposite direction, a circuit foractuating the potentiometer in one direction vwhich includes the firstcontact piece, the needle and the resistance, and a circuit foractuating the potentiometer in the opposite direction which includes thesecond contact piece, the needle and the resistance.

5. In a device of the class described, the combination with apotentiometer, of electrical means for actuating the potentiometer inone direction, electrical meansfor actuating the potentiometer in theopposite direction, a galvanometci having a pivoted coiland anindicating needle, a resistance, a circuit which includes thepotentiometer, the resistance and the pivoted coil, a contact piece withwhich the needle make-s electrical contact when deflected in onedirection, a battery of a given polarity, a circuit which includes thefirst electrical means, the battery, the contact piece, the needle andthe resistance, a second contact piece with which the needle makeselectrical contact when defiected in the opposite direction, a batteryof opposite polarity, anda circuit which includes the second `electricalmeans, the second battery, the second contact piece, the indicatingneedle and the resistance.

6. In. a device of the class described, the combination with an electricswitch, of a sec ond electric switch, electro-magnetic. means Lforsimultaneously' closing the first switch and opening the second switch,a spring for simultaneously opening the first switch and closing thesecond switch when the electromagneticmeans is deenergized, a thirdelectrical switch, a fourth electrical switch, electromagnetic means forsimultaneously closing the third switch and opening the secondv switch,a spring for simultaneously opening the third and closing the fourthswitch whenu the second electromagnetic means is deenergized, agalvanometer having a pivoted coil and an indicating needle, aresistance, a cir.- cuit which includes the resistance, and theA,pivoted coil, a contact piece'with which the needle makes contact whendefiected in one direction, a battery of given polarity, a circuit whichincludes the battery, the contact piece, the needle, the resistance, thesecond switch and the first electromagnetic means, a second contactpiece with which the needlemakes contact when deflected in the oppositedirection, a second battery of opposite olarity, a circuit whichincludes the secon battery, the second contact piece, the needle, the

resistance, the fourth switch and the second electromagnetic. means, apotentiometer, electrical means for actuating the potentiometer in onedirection, a second electrical means for actuating the potentiometer inthe opposite direction, a circuit which includes the first electricalmeans and the first electric switch, and a circuit which includes thesecond electrical means and a third electric switch.

7 In a device of the class described, the combination with an electricswitch, of a second electric switch, electromagnetic means forsimultaneously closing the first switch and opening the second switch, aspring for simul taneously opening the first switch and closing thesecond switch when the electromagnetic means is deenergized, a thirdelectrical switch, a fourth electrical switch, electromagnetic means forsimultaneously closing the third switch and opening the fourth switch, aspring for simultaneously opening the third and closing the fourthswitch when `the second electromagnetic means is deenergized, agalvanometer having a pivoted coil and an indicatingv needle, aresistance, a potentiometer, a circuit which includes the resistance,the potentiometer and the pivoted ond contact piece with which theneedle makes contact when deflected in the opposite direction, asecondbattery of opposite polarity, a circuit'which includes the secondbattery, the second contact piece, the needle, the resistance, thefourth switch and the second electromagnetic means, electrical means foractuating the potentiometer in one direction, a second electrical meansfor actuating the potentiometer inthe opposite direction, a circuitwhich includes the first electrical means and the'first electric switch,and a circuit which includes the second electrical means .and a thirdelectric switch.

a in a device of the dass described, the

combination with a cylinder, of a wire wound on the cylinder andelectrically insulated from it, a ring on the cylinder with which oneend of the wire is electrically connected, a second ring on the cylinderwith which the other end of the'wire is electrically connected, a thirdring on the cylinder with which a point on the wire between its two endsis electrically connected, a battery, an adjustable resistance, anammeter, a circuit which includes the first ring, the wire, the secondring, the batt-ery, the adjustable resistance and the ammeter, anelectric contact shoe which rests against the wire, means for shit-' ingthe shoe in either direction. along the length of the wire, agalvanometer, and a circuit which includes the galvanometer, the thirdring and the shoe.

9. In a device of the class described, the

combination with a cylinder, of a wire wound on the cylinder andelectrically insulated from it, a ring on the cylinder with which oneend of the wire is electrically connected,

` a second ring on the cylinder with which the (ill other end of thewire is electrically connected, a third ring on the cylinder with whicha point on the wire between its two ends is electrically connected, abattery, an adjust able resistance, an ammeter, a circuit whichincludesthe first ring, the wire, the second ring; thel battery, theadjustable resistance and the ammeter, a shoe with a groove that fitsover the wire substantially as described, a spring for pressing theshoeagainst the wire, a guide for limiting the motion of the shoe to a,single direction parallel to the axis of the cylinder, means forrotating the cylin-4 der in either direction, a galvanometer forcontrolling the rotating means substantially as described, and a circuitwhich includes the galvanometer, the shoe, and the third ring.

10. In a device of the class described. the combination with a cylinder,of a-thread on the cylinder consisting of a spirally wound wire, a shoewith a groove to fit the thread, means for moving the shoe along thethread in either direction, a ring on the cylinder electricallyconnected with one end of the thread, a second ring on the cylinderelectrically connected with the other end of the thread, a third ring onthe cylinder electrically connected with the thread at a point betweenits two ends, an electric circuit which includes the thread, the firstring and the second ring, and an electric circuit which includes theshoe, the third ring and the thread between 'the third ring and theshoe.

ll. In a. device of the class described, 'the combination with acylinder, of means for rotating the cylinder on its axis, a thread onthe cylinder. consisting of a wire spirally wound on and insulated fromthe cylinder, a shoe with a groove to fit the thread, a guide forpreventing the revolving of the shoe about the axis of the cylinder, aring on the cylinder electrically connected with one end of the thread,`a second ring on the cylinder electrically connected with the other endof the thread, a third ring on the cylinder electrically connected withthe thread at a point between its two ends, a brush for makingelectrical contact with the first ring, a second brush for makingelectrical contact with the second ring, a third brush for makingelectrical contact with the third ring, a variable resistance, abattery, an ammeter, acircuit which includes the variable resistance,the battery, the ammeter, the first brush, the first ring, the thread,the second ring andthe second brush, a galvanometer for controlling therotating means, and a circuit which includes the galvanometer, the shoe,the third ring, the third brush and the thread between the third ringand the shoe.

12. In a device of the class described, the combination with a cylinder,of electrical means for rotating the cylinder in one direction,electrical means forv rotating the cylinder in the opposite direction, athread on the cylinder consisting of a wire spirally Wound on andinsulated from the cylinder, a shoe with a groove to fit the thread,means for pressing the shoe against the thread, a guide for limiting themotion of the shoe to a fixed l path parallel to the axis of thecylinder, a

ring on' the cylinder electrically connected with one end of the thread,a second ring on the cylinder' electrically Aconnected with the otherend of the thread, a, third ring on the cylinder electrically connectedwith the thread at a fixed point between its two ends, a brush formaking electrical contact with the first ring, a second similar brushfor the second ring, a third similar brush for the third ring, anelectric circuit which includes the iirst brush, the first ring, thethread, the second .ring and the second brush, a galvanometer, anelectrical resistance, an electric circuit which includes thegalvanometer,the

resistance, the third brush, the third ring, the

shoe and the thread between the third ring and the shoe, an electriccircuit which includes the resista-nce and the first rotating means, andan electric circuit which includes the resistance and the secondrotatino' means.

rarrz FREDERICK UEHING.

